This invention relates to an improved radial blanket for the cores of nuclear reactors, particularly pressurized water reactors (PWR).
Nuclear reactors have a grouping of fuel assemblies in an array termed the core. The fuel assemblies each comprise an array of cylindrical rods containing fissile fuel. Energy is produced in the reactor by neutron-induced fission reactions in the fuel.
The array of fuel assemblies forms a structure which is approximately a right circular cylinder. The fuel assemblies located on the perimeter of the core may have characteristics which in the industry cause these assemblies to be termed "radial blanket" assemblies.
The application of radial blankets of fertile material to the periphery of PWR cores has been studied extensively. The principal goal of conventional blankets has been to capture neutrons that would otherwise have escaped the fuel core in fertile material, thereby producing fissile material. The impediment to this strategy which has prohibited the use of these blankets in PWR's to date is power peaking that results inboard in the core. This power peaking is the result of displacing peripheral fuel assemblies of enriched fuel with low reactivity, fertile material. The conclusion which has been reached repeatedly in the industry is that the resulting power peaking is unacceptable. Other attempts to successfully install radial blankets in PWR's have employed radical fuel design or core structure changes, e.g., installing fertile material in the zone between a core baffle and barrel or reducing the fuel assembly size by a factor of four to permit installation of smaller fertile assemblies around the periphery. These alternatives are accompanied by departures from existing core designs which are not merited by the resulting neutron utilization improvement. The application of radial blankets in boiling water reactors (BWR's) has been successful primarily due to the already reduced size of BWR fuel assemblies (about 1/4 of PWR size).
Consequently, it is desired to provide a design for a blanket assembly that can be used to capture neutrons at the core perimeter, reducing core leakage, with an acceptable core power peaking factor.